System and method for detection of degradation of vacuum brake booster sensor

ABSTRACT

Systems and methods for detecting degradation of a sensor in a vacuum brake booster coupled to a manifold of an internal combustion engine include measuring an engine or vehicle operating parameter to detect operating or control conditions and detecting degradation of the sensor based on the engine or vehicle operating parameter. In one embodiment the operating parameter is a measured or estimated manifold pressure. A pressure drop across a check valve disposed between the brake booster and the intake manifold may also be considered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/838,799, filed on Apr. 20, 2001, entitled “System and Method forDetection of Degradation of Vacuum Brake Booster Sensor”, which is acontinuation-in-part of U.S. application Ser. No. 09/479,173, filed Jan.7, 2000, titled “Estimation Method”, both assigned to the same assigneeas the present application, and incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to internal combustion engines havingvacuum assisted brake systems.

2. Background Art

Internal combustion engines are known that improve thermal efficiencyand reduce pumping work by operating lean of stoichiometry andincreasing manifold pressure. It is also known to extend lean operationby performing stratified operation where fuel is injected directly intothe engine cylinder during a compression stroke. These engines are alsocapable of performing homogeneous operation where fuel is injectedduring an intake, or suction, stroke. Typically, stratified operation islimited to lean air/fuel ratios, while homogeneous operation can be bothlean and rich of stoichiometry.

Vehicle brake systems are also known that use vacuum assist to increasedriver braking force. In these systems, vacuum generated by engineoperation provides extra force to assist driver braking. When thesebraking systems are combined with lean burn engines, engine operationcan be controlled so that desired vacuum is supplied during braking. Oneapproach uses a vacuum pressure sensor located in a brake booster toindicate available braking vacuum. When available vacuum falls below apredetermined value, engine air/fuel ratio is decreased towardstoichiometry and stratified operation is discontinued. Vacuum sensordegradation is determined when sensor voltage is outside a predeterminedrange of acceptable limits. Such a system is described in U.S. Pat. No.5,826,559.

The inventors herein have recognized a disadvantage with the aboveapproach. In particular, in-range sensor degradation is not addressed inthe above system. For example, if the sensor indicates insufficientvacuum when sufficient vacuum is present, the engine air/fuel ratio isunnecessarily decreased and fuel economy can be degraded. In otherwords, the prior art does not monitor such a situation.

SUMMARY OF THE INVENTION

An object of the present invention is to determine degradation of avacuum sensor coupled to a vacuum brake booster.

The above object is achieved and disadvantages of prior approachesovercome by a method for determining operability of a sensor in a vacuumbrake booster coupled through a check valve to a manifold of an internalcombustion engine, the method comprising: measuring or estimating anengine or vehicle operating parameter; and determining degradation inthe brake booster sensor based on said operating parameter.

By using other operating parameters as an indication of operation, it ispossible to determine in-range sensor degradation. In other words,system redundancy is exploited to extract information provided by otherengine and/or vehicle sensors to determine in-range sensor degradation.

An advantage of the above aspect of the present invention is thatimproved fuel economy can be achieved by more accurately selectingdesired engine combustion modes.

In another aspect of the present invention, the above object is achievedand disadvantages of prior approaches overcome by a method fordetermining operability of a sensor in a vacuum brake booster coupledthrough a check valve to a manifold of an internal combustion engine ina vehicle system, the method comprising: determining that a brakingcycle has been completed based on vehicle information; and determiningdegradation in the sensor when the sensor value changes by less than apredetermined amount during said braking cycle.

By using vehicle information to determine a braking cycle, it ispossible to determine that brake booster pressure should have changed.When a change is not detected, degradation can be determined. Thus, fromthe vehicle information, it is possible to determine in-range sensordegradation.

An advantage of the above aspect of the present invention is thatimproved fuel economy can be achieved by more accurately selectingdesired engine combustion modes. In yet another aspect of the presentinvention, the above object is achieved and disadvantages of priorapproaches overcome by a method for determining operability of a sensorin a brake booster coupled through a check valve to a manifold of aninternal combustion engine, the sensor measuring a pressure in the brakebooster, the method comprising: calculating a manifold pressure; anddetermining degradation in the sensor when the brake booster pressure isgreater than said manifold pressure by a predetermined amount.

By comparing manifold pressure to brake booster pressure, degradationcan be determined when brake booster pressure is greater than manifoldpressure. In other words, since the check valve prevents flow fromentering the brake booster and only allows flow to exit the brakebooster when manifold pressure is less than brake booster pressure, whenbrake booster pressure is indicated to be greater than manifoldpressure, in-range sensor degradation can be detected.

An advantage of the above aspect of the present invention is thatimproved fuel economy can be achieved by more accurately selectingdesired engine combustion modes.

Another advantage of the above aspect of the present invention is thatdegradation can be detected at many times during vehicle operation.

Other objects, features and advantages of the present invention will bereadily appreciated by the reader of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and advantages of the invention claimed herein will be morereadily understood by reading an example of an embodiment in which theinvention is used to advantage with reference to the following drawingswherein:

FIG. 1 is a block diagram of an embodiment in which the invention isused to advantage; and

FIGS. 2-16 are high level flowcharts describing a portion of operationof the embodiment shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Direct injection spark ignited internal combustion engine 10, comprisinga plurality of combustion chambers, is controlled by electronic enginecontroller 12. Combustion chamber 30 of engine 10 is shown in FIG. 1including combustion chamber walls 32 with piston 36 positioned thereinand connected to crankshaft 40. In this particular example, piston 30includes a recess or bowl (not shown) to help in forming stratifiedcharges of air and fuel. Combustion chamber 30 is shown communicatingwith intake manifold 44 and exhaust manifold 48 via respective intakevalves 52 a and 52 b (not shown), and exhaust valves 54 a and 54 b (notshown). Fuel injector 66 is shown directly coupled to combustion chamber30 for delivering liquid fuel directly therein in proportion to pulsewidth of signal fpw received from controller 12 via conventionalelectronic driver 68. Fuel is delivered to fuel injector 66 by aconventional high pressure fuel system (not shown) including a fueltank, fuel pumps, and a fuel rail.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of throttle plate 62is controlled by controller 12 via electric motor 94. This configurationis commonly referred to as electronic throttle control (ETC) which isalso utilized during idle speed control. In an alternative embodiment(not shown), which is well known to those skilled in the art, a bypassair passageway is arranged in parallel with throttle plate 62 to controlinducted airflow during idle speed control via a throttle control valvepositioned within the air passageway.

Exhaust gas oxygen sensor 76 is shown coupled to exhaust manifold 48upstream of catalytic converter 70. In this particular example, sensor76 provides signal UEGO to controller 12 which converts signal UEGO intoa relative air/fuel ratio λ. Signal UEGO is used to advantage duringfeedback air/fuel control in a conventional manner to maintain averageair/fuel at a desired air/fuel ratio.

Conventional distributorless ignition system 88 provides ignition sparkto combustion chamber 30 via spark plug 92 in response to spark advancesignal SA from controller 12.

Controller 12 causes combustion chamber 30 to operate in either ahomogeneous air/fuel mode or a stratified air/fuel mode by controllinginjection timing. In the stratified mode, controller 12 activates fuelinjector 66 during the engine compression stroke so that fuel is sprayeddirectly into the bowl of piston 36. Stratified air/fuel layers arethereby formed. The stratum closest to the spark plug contains astoichiometric mixture or a mixture slightly rich of stoichiometry, andsubsequent strata contain progressively leaner mixtures. During thehomogeneous mode, controller 12 activates fuel injector 66 during theintake stroke so that a substantially homogeneous air/fuel mixture isformed when ignition power is supplied to spark plug 92 by ignitionsystem 88. Controller 12 controls the amount of fuel delivered by fuelinjector 66 so that the homogeneous air/fuel mixture in chamber 30 canbe selected to be at stoichiometry, a value rich of stoichiometry, or avalue lean of stoichiometry. The stratified air/fuel mixture will alwaysbe at a value lean of stoichiometry, the exact air/fuel being a functionof the amount of fuel delivered to combustion chamber 30. An additionalsplit mode of operation wherein additional fuel is injected during theexhaust stroke while operating in the stratified mode is available. Anadditional split mode of operation wherein additional fuel is injectedduring the intake stroke while operating in the stratified mode is alsoavailable, where a combined homogeneous and split mode is available.

Nitrogen oxide (NOx) absorbent or trap 72 is shown positioned downstreamof catalytic converter 70. NOx trap 72 absorbs NOx when engine 10 isoperating lean of stoichiometry. The absorbed NOx is subsequentlyreacted with HC and catalyzed during a NOx purge cycle when controller12 causes engine 10 to operate in either a rich homogeneous mode or astoichiometric homogeneous mode.

Exhaust gas recirculation tube 120 is also shown coupled between intakemanifold 44 and exhaust manifold 48. Exhaust gas recirculation valve 122is placed in exhaust gas recirculation tube 120 to control an amount ofrecycled exhaust flow. Sensor 124 indicates EGR flow ({tilde over(m)}_(egr)).

Vacuum brake booster 130 is also shown fluidly communicating withmanifold 44 via tube 132. Check valve 134 is placed in tube 132 to allowair to pass from vacuum brake booster 130 to manifold 44 only whenmanifold pressure ({tilde over (p)}_(m)) is less than brake boosterpressure ({tilde over (p)}_(bb)). Thus, check valve 134 allows vacuum tobe retained in vacuum brake booster 130 even when manifold pressure({tilde over (p)}_(m)) is higher than brake booster pressure ({tildeover (p)}_(bb)). Vacuum brake booster 130 is also coupled to hydraulicbrake system 136 and brake pedal 138. Brake pedal position is measuredvia sensor 140 and provides signal ({tilde over (θ)}_(b)), whichrepresents position of brake pedal 138. In this example, sensor 140provides a continuous signal that allows determination of brake pedalposition throughout an entire span. However, sensor 140 can also providea switch signal that represents when brake pedal 138 has traveled past apredetermined distance. Sensor 142 provides an indication of brakebooster pressure ({tilde over (p)}_(bb)). In this example, sensor 142provides a continuous signal that allows determination of brake boosterpressure throughout an entire span. However, sensor 142 can also providea switch signal asserted when brake booster pressure has reached apredetermined value. Sensor 144 provides an indication of hydraulicbrake pressure ({tilde over (p)}_(h)). In this example, sensor 144provides a continuous signal that allows determination of hydraulicbrake pressure throughout an entire span. However, sensor 144 can alsoprovide a switch signal asserted when hydraulic brake pressure hasreached a predetermined value.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, anelectronic storage medium for executable programs and calibrationvalues, shown as read-only memory chip 106 in this particular example,random access memory 108, keep alive memory 110, and a conventional databus.

Controller 12 is shown receiving various signals from sensors coupled toengine 10, in addition to those signals previously discussed, including:measurement of inducted mass airflow ({tilde over (m)}_(air)) from massairflow sensor 100 coupled to throttle body 58; engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a profile ignition pickup signal (PIP) from Hall effect sensor 118coupled to crankshaft 40; throttle position ({tilde over (θ)}_(t)) fromthrottle position sensor 120; and absolute Manifold Pressure Signal({tilde over (p)}_(m)) from sensor 122. Engine speed signal (Ñ) isgenerated by controller 12 from signal PIP in a conventional manner, andmanifold pressure signal ({tilde over (p)}_(m)) provides an indicationof engine load. Note that the symbol {tilde over ()} is used tospecifically indicate a measured variable when necessary, while thesymbol is {circumflex over ( )} used to specifically indicate anestimate when necessary. Variables without either signal may represent ameasured or estimated value.

In this particular example, temperature Tcat is provided by temperaturesensor 124 and temperature Ttrp is provided by temperature sensor 126.However, those skilled in the art will recognize that these values maybe estimated rather than measured.

Also, i is an index that occurs at execution of computation looprepresenting either fixed or variable sample time or engine firings, andk is an index representing driving cycles.

Estimating Brake Booster Pressure from Other Parameters

The following figures describe methods according to the presentinvention for estimating brake booster pressure based on otherparameters.

Referring now to FIG. 2, a routine is described for estimating brakebooster pressure from measured manifold pressure ({tilde over (p)}_(m))and a brake actuation signal. In step 210, a determination is made as towhether a braking cycle has been completed. A braking cycle isdetermined from brake actuation signal. The brake actuation signal canbe generated from brake pedal position ({tilde over (θ)}_(b)), orhydraulic brake pressure ({tilde over (p)}_(h)). In other words, eitherof these signals can be used to determine when the brakes have beenapplied and released and an amount of vacuum has been consumed by vacuumbrake booster 130. For example, if brake pedal position ({tilde over(θ)}_(b)) is a switch, cycling of this switch can be used as anindication that a braking cycle has been detected. Further, if brakepedal position ({tilde over (θ)}_(b)) is a continuous signal, when thissignal goes back and forth across a certain level, this can be used toindicate that a braking cycle has been detected. Still other methods canbe used for determining brake actuation, such as, for example, hydraulicbrake pressure, displacement hydraulic braking actuators, or parametersof electric brake actuators.

Continuing with FIG. 2, when a braking cycle has been detected, theroutine continues to step 212 where temporary estimated brake boosterpressure ({circumflex over (p)}_(bb) ^(t)) is set equal to previouslyestimated brake booster pressure ({circumflex over (p)}_(bb) ^(i−1)) andpredetermined value G. Predetermined value G represents an amount ofvacuum, or pressure, that is used by vacuum brake booster 130 whenactuating the braking system. Otherwise, in step 214, temporaryestimated brake booster pressure ({circumflex over (p)}_(bb) ^(t)) isset equal to previously estimated brake booster pressure ({circumflexover (p)}_(bb) ^(i−1)) Next, in step 216, a determination is made as towhether temporary estimated brake booster pressure ({circumflex over(p)}_(bb) ^(t)) is greater than measured manifold pressure ({tilde over(p)}_(m)). When the answer to step 216 is YES, current estimated brakebooster pressure ({circumflex over (p)}_(bb) ^(i)) is set equal tomeasured manifold pressure ({tilde over (p)}_(m)) minus predeterminedvalue H. Predetermined value H represents the pressure drop across checkvalve 134. Otherwise, in step 220, the current estimated brake boosterpressure ({circumflex over (p)}_(bb) ^(i)) is set equal to temporaryestimated brake booster pressure ({circumflex over (p)}_(bb) ^(t)).Thus, according to the present invention, it is possible to estimatebrake booster pressure using other operating parameters. In particular,by including the pressure drop across the valve, a more accurateestimate is provided.

Referring now to FIG. 3, a routine is described for estimating brakebooster pressure using braking system parameters and an estimatedmanifold pressure ({circumflex over (p)}_(m)) In step 310, adetermination is made as to whether a braking cycle has been completedas described previously with respect to step 210. When a braking cyclehas been detected, the routine continues to step 312 where estimatedtemporary brake booster pressure ({circumflex over (p)}_(bb) ^(t)) isset equal to the previously estimated brake booster pressure({circumflex over (p)}_(bb) ^(i−1)) and predetermined value G.Predetermined value G represents an amount of vacuum, or pressure, thatis used by vacuum brake booster 130 when actuating the braking system.Otherwise, in step 314, temporary estimated brake booster pressure({circumflex over (p)}_(bb) ^(t)) is set equal to the previouslyestimated brake booster pressure ({circumflex over (p)}_(bb) ^(i−1)). Instep 315, manifold pressure is estimated from other engine parametersusing function g and parameters: {tilde over (m)}_(air), {tilde over(m)}_(egr), and Ñ. Those skilled in the art will recognize various othermethods for estimating manifold pressure using these or otherparameters, including modifications for temperature, heat transfer, andvarious other corrections.

Next, in step 316, a determination is made as to whether temporaryestimated brake booster pressure ({circumflex over (p)}_(bb) ^(t)) isgreater than estimated manifold pressure ({circumflex over (p)}_(m)).When the answer to step 316 is YES, current estimated brake boosterpressure ({circumflex over (p)}_(bb) ^(i)) is set equal to the estimatedmanifold pressure ({circumflex over (p)}_(m)) minus predetermined valueH as represented by step 318. Predetermined value H represents thepressure drop across check valve 134. Otherwise, in step 320, thecurrent estimated brake booster pressure ({circumflex over (p)}_(bb)^(i)) is set equal to the temporary estimated brake booster pressure({circumflex over (p)}_(bb) ^(t)). Thus, according to the presentinvention, it is possible to estimate brake booster pressure using otheroperating parameters.

According to the present invention, the estimated brake booster pressuredescribed above can be used for engine and vehicle control. For example,estimated brake booster pressure can be used to determine a desiredcombustion mode. In particular, estimated brake booster pressure can beused to disable lean or stratified combustion when estimated brakebooster pressure is greater than a predetermined pressure value.

Those skilled in the art will recognize, in view of this disclosure,that the methods for estimating brake booster pressure can also be usedto improve measurements of brake booster pressure. Thus, improvedaccuracy can be obtained.

Estimating Other Parameters from Brake Booster Pressure

The following figures describe methods according to the presentinvention for estimating parameters based on brake booster pressure.

Referring now to FIG. 4, a routine is described for estimating manifoldpressure based on brake booster pressure. First, in step 410, adetermination is made as to whether measured brake booster pressure({tilde over (p)}_(bb)) is decreasing. In a preferred embodiment, thisis performed by comparing successive measurements of brake boosterpressure to one another. When it is determined that brake boosterpressure is decreasing, the routine continues to step 412. In step 412,manifold pressure is estimated based on measured brake booster pressure({tilde over (p)}_(bb)) and predetermined value H. Predetermined value Hrepresents pressure drop across check valve 134. Next, in step 412, aflag is set to KNOWN. Otherwise, the routine continues to step 415,where the flag is set to UNKNOWN. In other words, estimated manifoldpressure ({circumflex over (p)}_(m)) can be determined from the brakebooster pressure whenever the measured brake booster pressure isdecreasing. Those skilled in the art will recognize various othermethods of determining if brake booster pressure is decreasing. Forexample, various different filtering techniques can be used such as highpass filtering and low pass filtering. Also, limit values can be used todetermine when brake booster pressure is decreasing greater than apredetermined value, and only inferring manifold pressure from brakebooster pressure when it is decreasing greater than this predeterminedvalue. Those skilled in the art will recognized various methods ofdetermining whether a parameter is decreasing, or decreasing by apredetermined amount, or decreasing at a predetermined rate.

Referring now to FIG. 5, a routine is described for estimating manifoldpressure based on measured brake booster pressure as well as otherparameters. First, in step 510, a determination is made as to whetherthe flag equals KNOWN. When the answer to step 510 is NO, value L is setequal to zero in step 512. Otherwise, in step 514, value L is determinedas a function of measured brake booster pressure ({tilde over (p)}_(bb))and a previously estimated manifold pressure ({circumflex over (p)}_(bb)^(i−1)) as well as value H. Then, in step 516, the current estimatedmanifold pressure ({circumflex over (p)}_(m) ^(i)) is based on previousestimated manifold pressure ({circumflex over (p)}_(bb) ^(i−1)) as wellas measured mass airflow ({tilde over (m)}_(air)) and engine speed (Ñ)and value L. Thus, according to the present invention, it is possible toestimate manifold pressure using other parameters such as mass airflowand engine speed, and then correct this estimate based on measured brakebooster pressure whenever brake booster pressure is decreasing. Anadvantage of this aspect of the present invention is that it is possibleto accurately estimate manifold pressure even when brake boosterpressure is not decreasing. Also, parameters A and B are systemparameters which represent the system dynamics and input dynamics as isknown to those skilled in the art. Also, value L can be learned inmemory as a function of engine speed and engine load. Again, value Lrepresents the error between the estimate using other variables and theestimate using the brake booster pressure. Value L also represents whatis known to those skilled in the art as an observer structure. Also,functions can be a simple gain, or the sign function, or many otherfunctions known to those skilled in the art of estimators, observers,and modern estimation theory.

In an alternative embodiment, where manifold pressure is estimated basedon measured mass airflow and engine speed, this estimate can be clippedso that it does not go below measured brake booster pressure. Also, thisvalue that is clipped can be learned and stored in memory and then canbe used everywhere to correct the estimated manifold pressure. In otherwords, whenever the estimated manifold pressure reads less than themeasured brake booster pressure, the error between the two is learnedand used to correct the estimated manifold pressure over the entireoperating range.

Referring now to FIG. 6, a routine is described for estimating otherengine operating parameters based on measured brake booster pressure({tilde over (p)}_(bb)). First, in step 610, a determination is made asto whether a flag equals KNOWN. If the answer to step 610 is YES, theroutine continues to step 612, where engine mass airflow is estimatedbased on measured brake booster pressure ({tilde over (p)}_(bb)) andmeasured engine speed (Ñ). In step 614, engine speed is estimated basedon measured brake booster pressure ({tilde over (p)}_(bb)) and measuredmass airflow ({tilde over (m)}_(air)). In step 616, throttle position isestimated based on measured brake booster ({tilde over (p)}_(bb))pressure and engine speed (Ñ). In step 618, EGR flow is estimated basedon measured brake booster pressure ({tilde over (p)}_(bb)), measuredmass airflow ({tilde over (m)}_(air)), and measured engine speed (Ñ).Those skilled in the art will recognize various other combinations,equations and approaches for estimating engine operating parametersbased on measured brake booster pressure in view of the presentinvention. For example, in step 616, measured mass airflow ({tilde over(m)}_(air)) can also be used to improve the throttle position estimate({circumflex over (θ)}_(t)).

FIG. 7A estimates brake system parameters from brake booster pressure.In other words, when a braking cycle is estimated, it is possible todetermine a predicted brake pedal position profile, or a predictedhydraulic brake pressure profile. For example, when a braking cycle isestimated, it is possible to determine that the brake pedal has beendepressed by a first predetermined amount and has also been released bya second predetermined amount. Similarly, it is possible to determinethat the hydraulic brake pressure reached a first predetermined amountand has also been released by a second predetermined amount.

Referring now to FIG. 7A, in step 710, a determination is made as towhether measured brake booster pressure is increasing. In thisparticular example, brake booster pressure is increasing when it isgreater than a previously measured brake booster pressure and apredetermined value J. However, those skilled in the art will recognizevarious other methods for determining whether brake booster pressure isincreasing such as, for example, high pass filtering brake boosterpressure, comparing the rate of change of brake booster pressure to alimit value rate of change, and various other methods. When the answerto step 710 is YES, a determination is made as to whether measured brakebooster pressure ({tilde over (p)}_(bb)) is relatively constantindicating that the brake actuation is completed. When the answer tostep 711 is YES, the routine determines that a braking cycle has beencompleted in step 712. In other words, the routine determines brakesystem operation based on increasing brake booster pressure. Therefore,it is possible to determine whether a braking cycle should have beenestimated from other braking system parameters such as, for example,brake pedal position or hydraulic brake pressure.

According to the present invention, the estimated operating parametersdescribed above herein can be used for engine and vehicle control. Forexample, estimated manifold pressure or mass airflow can be used todetermine desired fuel injection amounts, fuel injection timings,combustion modes ignition timings, exhaust gas recirculation amounts,and other engine control parameters. For example, to maintain a desiredair/fuel ratio, a fuel injection amount can be adjusted based onestimated airflow or manifold pressure based on the measured brakebooster pressure.

Referring now to FIG. 7B, a routine is described for calculating controlsignals based on estimated parameters, where the estimated parametersare based on measured brake booster pressure. In step 750, controlsignals CS1, CS2, and CS3 are calculated using functions h1, h2, and h3and estimated parameters, {circumflex over (p)}_(m), {circumflex over(m)}_(air), and {circumflex over (θ)}. Control signals CS1, CS2, and CS3can represent: a desired fuel injection amount, a desired ignitiontiming amount, a desired fuel injection timing, a desired throttleposition, or any other control signal known to those skilled in the artwhich may benefit from information regarding manifold pressure, massairflow, and/or throttle position.

Determining Degradation of Brake Booster Pressure Sensor

The following figures describe various methods that can be used alone orin combination to determine degradation of brake booster pressure sensor142.

Referring now to FIG. 8, a routine is described for determiningdegradation of brake booster pressure sensor 142 based on measuredmanifold pressure. The routine assumes that a check valve is properlyoperating. First, in step 810, a determination is made as to whethermeasured brake booster pressure is greater than the sum of measuredmanifold pressure and predetermined value K1. Value K1 represents themaximum amount of pressure drop across a properly functioning checkvalve. When the answer to step 810 is YES, counter C1 is incremented instep 812. Next, in step 814, a determination is made as to whethercounter C1 is greater than limit value E1. When the answer to step 814is YES, an indication is created in step 814 to indicate possibledegradation of sensor 142. Thus, according to the present invention, itis possible to determine degradation of brake booster pressure sensorbased on measured manifold pressure. In other words, since check valve134 only allows brake booster pressure to be less than manifoldpressure, degradation is determined when measured brake booster pressureis greater than an allowable maximum level based on manifold pressure.Thus, according to the present invention, degradation in measured brakebooster pressure can be accurately determined.

Referring now to FIG. 9, a routine for determining degradation in brakebooster pressure sensor 142 based on an indicated brake cycle isdescribed. First, in step 910, a determination is made as to whether abraking cycle has been determined. Braking cycle is determined asdescribed previously herein with reference to step 210. Next, when theanswer to step 910 is YES, a determination is made as to whetherpreviously measured brake booster pressure is less than previouslymeasured manifold pressure plus predetermined value K2. In other words,a determination is made as to whether it would be possible or likely forthe brake booster pressure to increase by a measurable amount knowingthe previously measured manifold pressure if the brakes were cycledbetween the current measurement and the previous measurement. If it isnot possible or unlikely for the brake booster pressure to increase dueto a braking cycle because of low manifold pressure and check valve 134,then the answer to step 912 is NO. Otherwise, the answer to step 912 isYES, and a determination is made in step 914 as to whether the currentmeasured manifold pressure is less than the previously measured brakebooster pressure. In other words, a determination is made as to whetherthe current measured manifold pressure has decreased below thepreviously measured brake booster pressure indicating that it is notdesirable to determine braking cycles from measured brake boosterpressure. Thus, when the answer to step 914 is NO, the routine continuesto step 916 to determine whether measured brake booster pressure hasincreased. In other words, in step 916, conditions are such that abraking cycle should have caused brake booster pressure to increasesince brake booster pressure is below manifold pressure. When brakebooster pressure is not increasing, the routine continues to step 917 toincrement counter C2. Next, in step 920, a determination is made as towhether counter C2 is greater than limit E2. When the answer to step 920is YES, an indication is provided in step 922. Thus, according to thepresent invention, it is possible to determine degradation in measuredbrake booster pressure sensor 142 based on measured manifold pressureand a determination of brake cycling. Those skilled in the art willrecognize that measured manifold pressure can be replaced in thisroutine by estimated manifold pressure from sensors such as, forexample, engine speed and mass airflow. Thus, according to the presentinvention, degradation in measured brake booster pressure is determinedwhen brake booster pressure does not approach manifold pressure whenmeasured brake booster pressure is less than measured manifold pressure.

Referring now to FIG. 10, a routine is described for determiningdegradation in brake booster pressure sensor 142 based on vehicleoperation. First, in step 1010, a determination is made as to whetherthe vehicle has been driven, in other words, whether the vehicle hasbeen started and driven over a predetermined speed or more than apredetermined distance. When the answer to step 1010 is YES, adetermination is made in step 1012 as to whether measured brake boosterpressure is changing. This can be done by determining whether measuredbrake booster pressure changes by a predetermined amount. Thispredetermined amount reduces or prevents the possibility of regularsensor noise and variation falsely indicating that measured brakebooster pressure is properly changing. When the answer to step 1012 isNO, counter C3 is incremented in step 1014. Next, in step 1016, adetermination is made as to whether counter C3 is greater than limitvalue E3. When the answer to step 1016 is YES, an indication is providedin step 1018. Continuing with FIG. 10, when the answer to step 1012 isYES, counter C4 is reset to zero in step 1020. Thus, according to thepresent invention, it is possible to determine degradation and measuredbrake booster pressure knowing that brake booster pressure should changeif the vehicle has been driven. Therefore, it is also possible to detectin-range sensor degradation.

Referring now to FIG. 11, a routine is described for determiningdegradation in brake booster pressure sensor 142 based on brakingoperation. First, in step 1110, a determination is made as to whether abraking cycle has been detected as described previously herein withrespect to step 210. When the answer to step 1110 is YES, braking cycleparameter k is incremented and the measured brake booster pressure atthis step is stored as represented in steps 1111 and 1112. Then, in step1114, a determination is made as to whether the absolute value of thedifference between successive measurements of measured brake boosterpressure after brake cycling is greater than value E5. When the answerto step 1114 is NO, the routine continues to step 1116. In step 1116, adetermination is made as to whether measured manifold pressure isgreater than value Ti. When the answer to step 1116 is NO, the routinecontinues to step 1118 where counter C5 is reset. Otherwise, in step1120, counter C5 is incremented and determined whether it is greaterthan limit value E6 in step 1122. When the answer to step 1122 is YES,an indication is provided in step 1124. In other words, if brake boosterpressure is not changing even after actuation of the brakes whenmanifold pressure is greater than a value T1, degradation is detected.

Referring now to FIG. 12, a routine is described for determiningdegradation in measured brake booster pressure based on braking cycles.First, in step 1210, a determination is made as to whether a brakingcycle has been completed as described previously herein with respect toFIG. 2 in step 210. When the answer to step 1210 is YES, a determinationis made as to whether measured brake booster pressure plus apredetermined value K2 is less than manifold pressure. Those skilled inthe art will recognize that manifold pressure can be measured from amanifold pressure sensor or estimated using parameters such as enginespeed and mass airflow. Alternatively, throttle position and enginespeed can be used. In other words, in step 1212, a determination is madeas to whether a brake cycling should cause brake booster pressure toapproach manifold pressure. When the answer to step 1212 is NO, counterC5 is reset in step 1216. Otherwise, in step 1214, counter C5 isincremented. Then, in step 1218, a determination is made as to whethercounter C5 is greater than limit value E5. When the answer to step 1218is YES, an indication is provided in step 1220. Thus, according to thepresent invention, degradation in measured brake booster pressure isdetermined when brake booster pressure does not approach manifoldpressure after a predetermined number of braking cycles. Thus, value K2represents a maximum amount of pressure drop across check valve 134 or amaximum amount of measurement error in both determining manifoldpressure and brake booster pressure that can be tolerated.

Determining Degradation of Other Sensors from Measured Brake BoosterPressure

The following figures describe various methods that can be used alone orin combination to determine degradation of operating parameter sensorsbased on measured brake booster pressure.

Referring now to FIG. 13, a routine is described for determiningdegradation of manifold pressure sensor 122 based on measured brakebooster pressure. First, in step 1310, a determination is made as towhether flag equals KNOWN. When the answer to step 1310 is YES, theroutine continues to step 1312 where a determination is made as towhether the absolute value of the difference between measured manifoldpressure and estimated manifold pressure from either step 412 or step516 is greater than maximum air value F1. When the answer to step 1312is YES, counter C6 is incremented in step 1314. Continuing with FIG. 13,in step 1316, a determination is made as to whether counter C6 isgreater than limit value E6. When the answer to step 1316 is YES, anindication is provided in step 1318. Thus, according to the presentinvention, it is possible to determine degradation of manifold pressuresensor 122 based on brake booster pressure sensor 142. In particular,even without estimating manifold pressure from measured mass airflow andengine speed or measured throttle position and engine speed, it is stillpossible to determine degradation of pressure sensor 122 by usingmeasured brake booster pressure whenever measured brake booster pressureis decreasing.

Referring now to FIG. 14, a routine is described for determiningdegradation in either brake pedal sensor or hydraulic brake pressuresensor using estimated brake cycling as described previously herein withrespect to FIGS. 7A and 7B. First, in step 1410, a determination is madeas to whether a brake cycle has been estimated as described previouslyherein with respect to FIG. 7A. When the answer to step 1410 is YES, theroutine continues to step 1412. In step 1412, a determination is made asto whether brake cycle has been determined from either brake pedalactuation or hydraulic brake pressure measurement as describedpreviously herein with respect FIG. 2. When the answer to step 1412 isNO, counter C7 is incremented in step 1414. Next, in step 1416, adetermination is made as to whether counter C7 is greater than limitvalue E7. When the answer to step 1416 is YES, an indication is providedin step 1418. Thus, according to the present invention, it is possibleto determine degradation in brake system sensors, such as brake pedalposition or hydraulic brake pressure, based on measured brake boosterpressure.

Referring now to FIG. 15, a routine is described for determiningdegradation in measured engine speed based on measured brake boosterpressure. First, in step 1510, a determination is made as to whether aflag equals KNOWN. When the answer to step 1510 is YES, then, asdescribed previously herein, it is possible to estimate engine speedfrom measured brake booster pressure and other operating parameters.When the answer to step 1510 is YES, the routine continues to step 1512,where the absolute value of the difference between measured engine speedand estimated engine speed determined from step 614 is greater than themaximum difference value F2. When the answer to step 1512 is YES, theroutine continues to step 1514 and increments counter C8. Next, in step1516, a determination is made as to whether counter C8 is greater thanlimit value E8. When the answer to step 1516 is YES, an indication isprovided in step 1518. Thus, according to the present invention, enginespeed estimated from brake booster pressure whenever brake boosterpressure is decreasing is used along with measured mass airflow todetermine degradation in engine speed sensing.

Referring now to FIG. 16, a routine is described for determiningdegradation in measured mass airflow based on measured brake boosterpressure. First, in step 1610, a determination is made as to whether aflag equals KNOWN. When the answer to step 1610 is YES, then, asdescribed previously herein, it is possible to estimate mass airflowfrom measured brake booster pressure and other operating parameters.When the answer to step 1610 is YES, the routine continues to step 1612,where the absolute value of the difference between measured mass airflowand estimated mass airflow determined from step 612 is greater than themaximum difference value F3. When the answer to step 1612 is YES, theroutine continues to step 1614 and increments counter C9. Next, in step1616, a determination is made as to whether counter C9 is greater thanlimit value E9. When the answer to step 1616 is YES, an indication isprovided in step 1618. Thus, according to the present invention, massairflow estimated from brake booster pressure whenever brake boosterpressure is decreasing is used along with measured engine speed todetermine degradation in mass airflow sensing.

Referring now to FIG. 17, a routine is described for determiningdegradation in throttle position based on measured brake boosterpressure. First, in step 1710, a determination is made as to whether aflag equals KNOWN. When the answer to step 1710 is YES, then, asdescribed previously herein, it is possible to estimate throttleposition from measured brake booster pressure and other operatingparameters. When the answer to step 1710 is YES, the routine continuesto step 1712, where the absolute value of the difference betweenmeasured mass airflow and estimated throttle position determined fromstep 616 is greater than the maximum difference value F4. When theanswer to step 1712 is YES, the routine continues to step 1714 andincrements counter C10. Next, in step 1716, a determination is made asto whether counter C10 is greater than limit value E10. When the answerto step 1716 is YES, an indication is provided in step 1718. Thus,according to the present invention, throttle position estimated frombrake booster pressure whenever brake booster pressure is decreasing isused along with measured engine speed to determine degradation inthrottle position sensing.

Referring now to FIG. 18, a routine is described for determiningdegradation in exhaust gas recirculation flow sensing based on measuredbrake booster pressure. First, in step 1810, a determination is made asto whether a flag equals KNOWN. When the answer to step 1810 is YES,then, as described previously herein, it is possible to estimate exhaustgas recirculation flow from measured brake booster pressure and otheroperating parameters. When the answer to step 1810 is YES, the routinecontinues to step 1812, where the absolute value of the differencebetween measured exhaust gas recirculation flow and estimated exhaustgas recirculation flow determined from step 618 is greater than themaximum difference value F5. When the answer to step 1812 is YES, theroutine continues to step 1814 and increments counter C11. Next, in step1816, a determination is made as to whether counter C11 is greater thanlimit value E11. When the answer to step 1816 is YES, an indication isprovided in step 1818. Thus, according to the present invention, exhaustgas recirculation flow estimated from brake booster pressure wheneverbrake booster pressure is decreasing is used along with measured massairflow and measured engine speed to determine degradation in exhaustgas recirculation flow sensing. Referring now to FIG. 19, a routine fordetermining degradation in either brake pedal position sensor 140 orhydraulic brake pressure 144 is described. First, in step 1910, adetermination is made as to whether a brake cycle has been determinedfrom the brake pedal or hydraulic brake pressure as described previouslyherein with respect to step 210. When the answer to step 1910 is YES, adetermine is made in step 1912 as to whether a braking cycle has beenestimated from measured brake booster pressure as previously describedherein with respect to FIG. 7A. When the answer to step 1912 is NO,counter C12 is incremented in step 1914. Next, in step 1916, adetermination is made as to whether counter C12 is greater than limitvalue E12. When the answer to step 1916 is YES, an indication isprovided in step 1918. Thus, according to the present invention, it ispossible to detect degradation in either brake pedal position sensor 140or hydraulic brake pressure sensor from measured brake booster pressure144.

Examples of Operation

The following figures describe graphs showing examples of operationaccording to the present invention as described above herein.

In FIG. 20, measured manifold pressure is shown with the estimated brakebooster pressure under normal operating conditions. The pressure dropacross the check valve H is indicated as well as the increase inpressure due to predetermined value G. Before time t0, brake boosterpressure is estimate directly from manifold pressure and H sincemanifold pressure is decreasing. Then, at time t1, the brakes areactuated. Then, at time t2, the brakes are released and it is determinedthat the brakes have been cycled and a predetermined value G is used torepresent the vacuum (or pressure) used by the brake booster.

In FIG. 21, estimated manifold pressure is shown using information fromboth measured airflow and engine speed, and from measured brake boosterpressure. Before time t3, manifold pressure is estimated from airflowand engine speed. Then, from time t3 to t4, where the flag is set toKNOWN, mass airflow, engine speed and measured brake booster pressureare used. As shown, the estimate from airflow and engine is correctedduring this time to improve the accuracy of estimated manifold pressure.Then, after time t4, only airflow and engine are again used.

In FIG. 22, degradation of measured brake booster pressure is described.At times t5, t6, t7, and t8, a braking cycle is completed as indicatedfrom brake pedal 140. As shown, measured brake booster pressure does notincrease during any of these braking cycles even though manifoldpressure is greater than the measured brake booster pressure. Thus,during each of these times, a counter increments. At time t8, thecounter has reached the calibrated level and an indication ofdegradation is provided.

This concludes a description of an example in which the invention isused to advantage. Those skilled in the art will recognize that manymodifications may be practiced without departing from the spirit andscope of the invention. For example, the present invention can be usedas a supplement to existing methods for estimating operating parametersand/or determining degradation. Also, the methods are not limited togasoline engines, but can be used with diesel engines, alternativelyfueled engines, or hybrid powertrains. Accordingly, it is intended thatthe invention be limited only by the following claims.

1-36. (canceled)
 37. A method for monitoring operability of a sensor ina vacuum brake booster coupled to a manifold of an internal combustionengine in a vehicle, the method comprising: determining whether thevehicle has been driven; monitoring changes in vacuum brake boosterpressure; determining whether the changes in vacuum brake boosterpressure exceed a predetermined amount. 38-44. (canceled)